Three-phase tap-changing transformer system

ABSTRACT

THE NUMBER OF GATE-CONTROLLED SEMICONDUCTOR A-C SWITCHING DEVICES (INVERSE PARALLEL CONNECTED THRYSTORS OR TRIACS) IN A THREE-PHASE TAP-CHANGING TRANSFORMER SYSTEM IS MINIMIZED BY SEQUENTIALLY USING THE SAME STATIC SEMICONDUCTOR SWITCHING DEVICES IN COMBINATION WITH APPROPRIATE SWITCHING DEVICES HAVING RELATIVELY MOVABLE CONTACTS FOR SEQUENTIALLY EFFECTING TAP-CHANGING OPERATIONS IN ALL THREE PHASES OF A Y-CONNECTED TRANSFORMER WHOSE WINDINGS ARE TAPPED.

Jan. 12, 1971 M. MATZL ETAL 3,555,403

THREE-PHASE TAP-CHANGING TRANSFORMER SYSTEM. Filed April 29, 1969 5 Sheets-Sheet 1 frigg er pulse generators 4/ I MAM/W, Ml/ J,

- Jan. 12, 1971, M mm ETA; 3,555,403

{THREE-PHASE TAP-CHANGING TRANSFORMER SYSTEM Filed April 29, 1969 5 Sheets-Sheet 2 {3 f3 flwrofs u) Jib/1 5/0 51/ 'W/W/L Mm f M M M /m Jan. 12, 1971. M 'T E IT 3,555,403

THREE-PHASE TAP-CHANGING TRANSFORMER SYSTEM Filed April 29, 1969 5 Sheets-Sheet S MMJ 1% M WW Mp/ Jan. 12, 1971 M. MATZL ETAL THREE-PHASE TAB-CHANGING TRANSFORMER SYSTEM s'sheets-sheet 4 Filed April 29, 1969 Mam raps;

r WW Mil/ aw w 31W] X4 Jan. 12, 1971 M. MATZL ETAL 3,555,403

THREE-PHASE TAP-CHANGING TRANSFORMER SYSTEM Filed April 29, 1969 5 Sheets-Sheet 5 Min/1. l 15f,

W X i/W) vA/Q/J W WMAXW United States Patent 3,555,403 THREE-PHASE TAP-CHANGIN G TRANSFORMER SYSTEM Manfred Matzl, Zeitlarn, Uber Regensburg, and Ulrich Schweitzer, Wenzenhach, Germany, assignors to Maschinenfabrik Reinhausen Gebruder Scheubeck K.G., Regensburg, Germany Filed Apr. 29, 1969, Ser. No. 820,151 Claims priority, application Germany, June 19, 1968, 1,763,529 Int. Cl. H02p 13/06; H02m /12 US. Cl. 323-435 12 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION Conventional tap-changing transformer systems include selector switches and transfer switches. The former prepare the circuits which are intended to be established, and the latter establish these circuits. This involves breaking of load currents. As a result, transfer switches are sub jected to arcing and their contacts to wear and erosion.

To avoid these limitations, various circuits have been evolved in recent times which include gate-controlled semiconductor A-C switching devices and are capable of performing tap-changing operations under load without occurrence of arcs between parting contacts, or engaging contacts. These various circuits are predicated on the application of at least two-gate-controlled semiconductor switching devices per phase, i.e. of two inverse parallel connected thyristors per phase, or two triacs per phase. Three-phase transformers therefore require three 2-3=6 gate-controlled semiconductor A-C switching devices, i.e. 6-2=12 back-to-back connected thyristors, or 6 triacs. The relatively large number of gate-controlled semiconductor A-C switching devices calls for a correspondingly large number of control means therefor, such as, for instance trigger pulse generators and associated parts. As a result the system as a whole is both complex and expensive.

This invention relates to the problem of reducing in a system of the kind under consideration the number of gate-controlled semiconductor A-C switching devices, thus drastically reducing the complexity and cost involved in the system.

SUMMARY OF INVENTION A three-phase tap-changing transformer system embodying this invention includes three tapped transformer windings each having at least a contiguous pair of taps, and means establishing a point Y-connecting said windings. The system further includes integral switch-means having two groups of relatively movable contacts for selectively conductively conducting one of said pair of taps ofall of said windings and the other of said pair of taps of all of said windings to said Y-connecting point and for sequentially disconnecting one of said pair of taps and connecting the other of said pair of taps of each of said windings to said Y-connecting point. The system further includes a first gate-controlled semiconductor A-C switch- "ice ing device having a pair of terminals in addition to the gate terminals thereof and a lead conductively connecting one of said pair of terminals of said first semiconductor A-C switching device to said Y-connecting point. The system further includes a first disconnect switch for selectively connecting the other of said pair of terminals of said first semiconductor A-C switching device to one of said pair of taps of each of said windings and for disconnecting said other of said pair of terminals of said first semiconductor A-C switching device from any taps of said Windings. The system further includes a second gate-controlled semiconductor A-C switching device having a pair of terminals in addition to the gate terminals thereof and a lead conductively connecting one of said pair of terminals of said second semiconductor A-C switching device to said Y-connecting point. The system further includes a second disconnect switch means for selectively connecting the other of said pair of terminals of said second semiconductor A-C switching device to the other of said pair of taps of each of said windings and for disconnecting the other of said pair of terminals of said second semiconductor A-C switching device from any tap of said windings.

While these are the basic components of a system embodying this invention, such a system further requires drive means for operating the aforementioned integral switch means and disconnect switch means at a high speed, and for controlling the triggering of the first and the second semiconductor A-C switching device as will be explained below more in detail.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram of a system embodying this invention showing the electrical connections of the constituent parts thereof.

FIG. 2 is a vertical section of the mechanical parts of a transfer switch forming a part of the system of FIG. 1;

FIG. 3 is a horizontal section along III-III of FIG. 2;

FIG. 4 is a horizontal section along IV IV of FIG. 2;

FIG. 5 is a horizontal section along V-V of FIG. 2;

FIG. 6 is a horizontal section along VIVI of FIG. 2;

FIG. 7 is a horizontal section along VII-VII of FIG. 2; and

FIG. 8 is a horizontal section along VIIIVIII of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION As shown in FIG. 1, a three-phase transformer includes three tapped phase windings U, V, W each having three contiguous taps 1, 2, 3. Actually the number of taps per winding is larger, but it is sufficient for a disclosure of this invention to merely consider two contiguous taps of windings U, V, W. Reference numerals 4, 5 have been applied to indicate cooperating pairs of selector switch contacts for connecting contiguous pairs of taps to a transfer switch. The selector switch does not need to be described in detail since such switches are well known in the art. See, for instance, US. Pat. 3,366,750 to A. Bleibtreu, June 30, 1968 for Switching Mechanism for Tapped Reggilating Transformers. The transfer switch includes a polyphase or three-phase change-over switch 6, tWo pairs of thyristors 7, 8 and 9, 10 and the polyphase or three-phase disconnect switches 11, 12. The change-over switch 6 is a current-carrying switch, i.e. its contacts are adapted to carry continuously currents of load current proportions. Fixed contacts 61, 62 of change-over switch 6 are conductively connected by leads and selector switch contacts 4, 5 to taps 1, 2 of winding U. In like fashion fixed contacts 63, 64 of switch 6 are conductively connected by leads and selector switch contacts 4, 5 to taps 1, 2 of winding V, and fixed contacts 65, 66 of switch 6 are conductively connected by leads and selector switch contacts 4, to taps 1, 2 of winding W. Change-over switch 6 has three radially outwardly extending contact arms 67, 68, 69 pivotable about fulcrum 13. The latter may form the neutral point of a Y-connection including the outgoing line Y. As an alternative contact arms 67, 68, 69 may be in permanent engagement with a fixed slip ring or annular contact as will be shown below more in detail whose center is fulcrum 13, in which case outgoing line Y is conductively connected to the aforementioned fixed slipring or annular contact. The fixed contacts 61-66 of change-over switch 6 encompass different angles or, in other words, differ in length. As a result, the time of engagement of the radially outer ends of pivotable contact arms 67, 68, 69 with their cooperating fixed contacts 61 to 66 differs depending upon the length of the latter.

Thyristors 7 and 8 are back-to-back connected, or inverse parallel connected, and the same applies as to thyristors 9, 10. Reference characters 71 and 72 have been applied to indicate a switching capacitor and a damping resistor, respectively, arranged in series with said capacitor and operatively related to the pair of thyristors 7, 8. Similarly reference characters 91 and 92 have been applied to indicate a switching capacitor and a damping resistor, respectively, arranged in series with said capacitor and operatively related to the pairs of thyristors 9, 10. Thyristors 7, 8 and 9, 10 have terminals in addition to the gate terminals thereof. Thyristors 7, 8 are a first gatecontrolled semiconductor switching device having a pair of terminals in addition to the gate terminals thereof and thyristors 9, 10 are a second switching device of the above description.

The disconnect switch 11 is provided with fixed contacts 111, 112 and 113 which are angularly displaced and whose angles of displacement differ. Contact 111 is conductively connected by a lead and contacts 4 to tap 1 of winding U, contact 112 is conductively connected by a lead and contacts 4 to tap 1 of winding V, and contact 113 is conductively connected by a lead and contacts 4 to tap 1 of winding W. The disconnect switch 12 includes fixed contacts 121, 122, 123 arranged in the same fashion as the fixed contacts 111, 112 and 113 of disconnect switch 11. Contact 121 is conductively connected by a lead and contacts 5 to tap 2 of winding U, contact 122 is conductively connected by a lead and contacts 5 to tap 2 of winding V, and contact 123 is conductively connected by a lead and contacts 5 to tap 2 of winding W. Disconnect switch 11 is provided with three angularly displaced contact arms 114,115 and 116 cooperating with fixed contacts 113, 114, 115 and pivotable about fulcrum 14. Fulcrum 14 is conductively connected by a lead to the left terminal of the pair of inverse parallel connected thyristors 7, 8. As an alternative, a fixed slip ring or annular contact arranged with fulcrum 14 as its center and permanently slidingly engaged by contact arms 114, 115, 116 may be conductively connected by a lead to the left terminal of the pair of inverse parallel connected thyristors 7, 8. An arrangement of this kind 'will be described below in connection with FIG. 2. Disconnect switch 12 is provided with three angularly displaced contact arms 124, 125, 126 cooperating with fixed contacts 121, 122, 123 and pivotable about fulcrum 15. Fulcrum 15 is conductively connected by a lead to the left terminal of the pair of inverse parallel connected thyristors 9, 10. As an alternative, a fixed slip ring or annular contact may be arranged with fulcrum 15 as its center and permanently slidingly engaged by contact arms 124, 125, 126 and be conductively connected by a lead to the left terminal of the pair of inverse parallel connected thyristors 9, 10. A modification of switch 12 of this character is described below in connection with FIG. 2.

While the left terminal of the pair of thyristors 7, 8 is conductively connected to fulcrum 14 of disconnect switch 11, the right terminal of thyristors 7, 8 is conductively connected by a lead to outgoing line Y. Similarly while the left terminal of the pair of thyristors 9, 10 is conductively connected by a lead to fulcrum 15 disconnect switch 12, the right terminal of thyristors 9, 10 is conductively connected by a lead to the outgoing line Y.

The control equipment of the tap-changing transformer system is energized by means of a power supply including the three auxiliary transformers 21, 22, 23. The primary windings of these auxiliary transformers are conductively connected to, and energized by, the three tapped transformer windings U, V, W. The primary winding of transformer 21 is conductively connected by the intermediary of leads including resistors 24 to taps 1, 2 of winding U, the primary winding of transformer 22 is conductively connected by the intermediary of leads including resistors 25 to winding V, and the primary winding of transformer 23 is conductively connected by leads including resistors 26 to winding W. The secondary windings of transformers 21, 22, 23 are Y-connected and energize a three-phase diode rectifier bridge 27. are the D-C output terminals of rectifier bridge 27 These terminals are shunted by two Zener diodes 28 and two capacitors 29 to mini- =mize ripple.

Control switch 30' includes a fulcrumed pivotable contact arm 33- Whose radially outer end cooperates or engages contacts 31, 32 arranged in a circular pattern. Contact arm 33 is conductively connected by means of a lead to the negative terminal of rectfier bridge 27. The fixed contacts of control switch 30 include odd contacts 31 alternating with even contacts 32. The contacts 31 are conductively interconnected and conductively connected by a lead to the input terminal E of a bistable circuitry 34, and the contacts 32 are conductively interconnected and conductively connected by a lead to the input terminal E of bistable circuitry 34. The output terminal A of bistable circuitry 34 is conductively connected by a lead to one input terminal of AND-gate 35, and the output terminal A of bistable circuitry 34 is conductively connected by a lead to one input terminal of AND-gate 36. The other input terminal of AND-gate 35 is conductively connected by a lead to voltage sensing device 38, and the other input terminal of AND-gate 36 is conductively connected by a lead to voltage sensing device 37. Voltage sensing device 38 includes a transformer 381, a resistor 383 arranged in series with the primary winding of transformer 38 1, a rectifier 382 energized by the secondary winding of transformer 381 and a Zener diode 384 connected across the D-C terminals of rectifier 382. The primary winding of transformer 381 and resistor 383 are connected to the terminals of inverse parallel connected thyristors 9, 10, i.e. shunted across thyristors 9, 10. In like fashion voltage sensing device 37 includes a transformer 371, a resistor 373 arranged in series with the primary winding of transformer 371, a rectifier 372 energized by the secondary winding of transformer 371 and a Zener diode 374 connected across the D-C terminals of re'ctifier 37,2. The primary winding of transformer 371 and resistor 373 are connected to the terminals of inverse parallel connected thyristors 7, 8, i.e. shunted across thyristors 7, 8. The output of AND-gate 35 controls a trigger pulse generator 39 and the output of AND-gate 36 controls a trigger pulse generator 40. Trigger pulse generators 39, 40' supply pulses for triggering thyristors 7, 8 and 9, 10. The output terminals 41a, 41b of generator 39 are intended to be conductively connected to the gate circuits of thyristors 7 and 8, and the output terminals 42a, 42b of generator 40 are intended to be conductively connected to the gate circuits of thyristors 9 and 10.

The system of FIG. 1 operates as follows:

Assuming that taps 2 of windings U, V, W are initially Y-connected and that it is intended to Y-connect taps 1 thereof. In the position of load-current-carrying changeover switch 6 shown in FIG. 1 the taps 2 of windings U, V, W are conductively connected to fixed contact segments 62, 64 and 66 and conductively connected by arms 67, 68 and 69 to fulcrum 13 and outgoing line Y, fulcrum 13 and outgoing line Y forming the neutral point of the Y-connected tapped transformer system. The disconnect switches 11, '12 are both open, i.e. their movable contact arms are out of engagement with their fixed contact segments. Hence no voltage appears across the pair of thyristors 7, '8 and the pair of thyristors 9, 10. Since there appears no voltage across these thyristors, there appears no voltage across the primary windings of transformers 371 and 381 and no signals are transmitted from rectifiers 372, 382 to AND-gates 36, 35. Therefore trigger pulse generators 39, 40 do not supply any thyristor trigger pulses. Such pulses are not generated unless either both inputs of AND-gate 35, or both inputs of AND-gate 36 are energized, but in the position of the constituent parts of the system shown in FIG. 1, this condition is not met.

In order to perform a tap-changing operation, switches 6, 11 and 12 are pivoted synchronously in counterclockwise direction, as indicated by three arrows in FIG. 1. When contact arm 126 of switch 12 engages fixed contact 123, the pair of thyristors 9, prepare a current path including lead 1' from tap 2 of winding W to neutral or outgoing line Y, which current path is parallel to the current path established by switch 6 to outgoing line Y including its cooperating contact 66, 69. As the counterclockwise pivotal motion of switches 6, 11, 12 continues, contact arm 116 of disconnect switch 11 engages the fixed contact segment 113 conductively connected by lead 2' to tap 2 of winding W. As a result, the voltage prevailing between taps 1 and 2 of winding W appears across the terminals of the pair of inverse parallel connected thyristors 7, 8. Hence transformer 317 of voltage sensing device 37 is energized, and the latter transmits a pulse to one of the inputs of the AND-gate 36, the magnitude of which pulse is limited by the action of Zener diode 374. The control switch connects by the intermediary of one of its fixed contacts 32 the negative terminal of diode rectifier bridge 27 to the input terminal E of bistable circuitry 34. Hence a voltage or signal appears at the output terminal A of bistable circuitry 34 and simultaneously at the input terminal of the AND-gate 36 conductively connected with output terminal A Since now both terminals of AND-gate 36 receive an input, the former initiates the operation of trigger pulse generator 40. Hence the latter triggers thyristors 9 and 10.

Now contact arm 69 of switch 6 parts from its cooperating fixed contact 66. As a result the load current derived from phase winding W is commutated or transferred to the pairs of thyristors 9, 10.

As the contact arms of switches 6, 11, '12 and 30 continue to pivot in counterclockwise direction, the contact arm 33 of switch 30 is moved from a contact of the group of contacts 32' to a contact of the group of contacts 31. As a result, the state of bistable circuitry 34 is changed, i.e. the voltage or signal at the output terminal A of bistable circuitry 34 disappears, and a voltage or signal appears at its output terminal A As a result, no trigger pulses are applied any longer to the pair of thyristors 9, 10. They continue, however, to carry the load current of the phase to which winding W pertains until the time of occurrence of a natural zero of the current wave. Following that time of natural current zero a voltage appears across the pair of thyristors 9, 10, energizing transformer 3 81 of voltage sensing device 38. Consequently both inputs of AND-gate 35 are simultaneously energized, causing initiation of the operation of trigger pulse generator 39. Hence thyristors 7 and 8 are triggered by generator 39. This establishes a current path for the load current of the phase associated with winding W from tap 1 of the latter, through lead 2, contacts 113, 116 and fulcrum 14 of switch 11 and the pair of thyristors 7, 8 to neutral or outgoing line Y.

As the tap-changing operation progresses contact 68 engages conta'ct segment 63 of change-over switch 6 and contact arm 126 of switch 12 parts from its cooperating fixed contact 123. Hence the pair of thyristors 9, 10 and transformer 381 are tie-energized. As a result triggering of the pair of thyristors 7, '8 is interrupted, and when contact arm 116 of switch 11 parts from its cooperating fixed contact 113, both pairs of thyristors 7, 8 and 9, 10 are disconnected from windings U, V, W are deenergized. This completes the tap-changing operation of phase winding W, and now the tap-changing operation of phase winding V tbegins.

Contact arm 33 of control switch 30' moves into engagement with one contact of the group of fixed contacts 32 and thus prepares triggering of thyristors 9 and 10. The contact arm 125 of disconnect switch 12 engages fixed contact 122, and thus prepares a current path from tap 2 of winding V through lead 3' and thyristors 9, 10 to the neutral point of the system or the outgoing line Y thereof. This current path is parallel to the current path from tap 2 of winding V through fixed contact segment 64 and contact arm 68 and fulcrum 13 of load-current-carrying switch 6 to the neutral point or the outgoing line Y. Upon engagement of fixed contact 112 of switch 11 by contact arm 115 the voltage across taps 2 and 1 of winding W is applied to thyristors 7 and 8 by the intermediary of lead 4. Hence transformer 371 of voltage sensing device 37 is energized and voltages are applied to both input terminals of AND-gate 36. This causes trigger pulse generator 40 to become operative and to supply trains of trigger pulses to the pair of thyristors 9, 10. Thereafter the tapchanging operation from tap 2 to tap 1 of winding W is completed in the same fashion as the operation of changing from tap 2 to tap 1 of phase winding V.

Briefly summarizing and recapitulating the above, it will be apparent that a tap-changing operation from tap 2 to tap 1 of winding W involves the following steps and that a tap-changing operation from taps 2 to taps 1 of windings V and U involve analogous steps.

(1) Initial position: Contacts 62, 67; 64, 68 and 66, 69 of change-over switch -6 Y-connect windings U, V, W, their respective taps 2 being included in the circuit. Disconnect switches 11, 12 are both open, disconnecting the left terminals of thyristors 7, 8 and 9, 10' from any tap of windings U, V, W. Transformers 371, 381 are deenergized and trigger pulse generators 39, 40 are inoperative.

(2) The contacts 126, 123 of disconnect 12 engage, preparing a current path from tap 2 of winding W through thyristors 9, 10 to Y parallel to the current path from tap 2 of winding W through contacts 66, 69 of change-over switch 6 to Y. There is no voltage across thyristors 9, 10 and transformer 381 remains deenergized.

(3) Contacts 116 and 113 of disconnect switch 11 engage, applying the dilference of potential between taps 2 and 1 of winding W across thyristors 7, 8, thus causing energization of transformer 371 and transmittal of a pulse from rectifier 372 to AND-gate 36. Simultaneously a pulse is transmitted by switch 30 to input E of bistable circuitry 34, and a pulse is transmitted from terminal A of bistable circuitry to AND-gate 36, causing operation of trigger pulses generator 40, and triggering of thyristors 9, 10. a

(4) Contacts 66, 69 of change-over switch 6 part, causing commutation or transfer of the entire current of phase winding W to the current path including contacts 123, 126 of disconnect switch 12 and thyristors 9, 10 to Y.

(5) Contact arm 33 of control switch 30 is moved to a contact of group 31 causing a change of state of bistable circuitry 34, i.e. the output voltage at terminal A disappears and an output voltage at terminal A appears. Disappearance of an output voltage at A causes interruption of the operation of trigger pulse generator 40, and thyristors 9, 10 become non-conductive. The voltage now appearing across thyristors 9, 10 energizes transformer 381, and rectifier 384 transmits a pulse to AND-gate 35 which initiates operation of trigger pulse generator 39, thus triggering thyristors 7, 8 and causing the load cur rent of winding W to flow through tap 1 thereof.

(6) Contacts 68 and 63 of change-over switch 6 engage, contacts 123, 126 of disconnect switch 12 disengage and open the circuit of thyristors 9, 10 causing deenergization of transformer 381, inoperativeness of trigger generator 39 and thus removal of trigger pulses from thyristors 7, 8.

(7) Contacts 113, 116 of disconnect switch 11 disengage. Now the current paths of both pairs of thyristors 7, 8 and 9, 10 is interrupted, the tap-changing operation of winding W completed and the tap-changing operation of winding V may start,

The steps involved in changing from tap 2 to tap 1 of phase windings V and U need not to be described in detail since they are analogous to the steps which have been described above in detail.

Tap-changing operations in reverse direction, i.e. from taps 1 of windings U, V, W to taps 2 of windings U, V, W are analogous to what has been described above, except that the sequence of tap-changes then is winding U, winding V, and winding W rather than winding W, winding V, and winding U.

Referring now to FIGS. 2-8, inclusive, numeral 50* has been applied to indicate the cover plate of a tank for housing a tapped transformer. Mounted on cover plate 50 is a frame structure 51 supporting motor drives and the transmissions for operating the selector switch and the transfer switch means of the transformer. The frame structure 52 supports a spring motor (not shown) intended for rapid operation of switches 6, 11, 12 and 30 diagrammatically illustrated in FIG. 1 and described in connection with this figure. The preferred structural embodiments of these switches will be described below in detail. Frame structure 51 supports an annular flange member 53 which, in turn, supports a cylindrical casing of insulating material, preferably of bakelized paper. The frame structure 52 for supporting the switch-operating spring motor (not shown) supports another cylindrical insulating casing 55 arranged within the upper portion of insulating casing 54 and in coaxial relation to the latter. Insulating casing 55 houses the two pairs of thyristors 7, 8 and 9, 10 and their control circuitry described in detail in connection with FIG. 1. Casing 55 is closed by a horizontal bottom portion having a circular aperture for the passage of insulating shaft 56. The latter supports on its lower end a metal shaft 57 for operating movable contacts of switching devices 6, 11 and 12.

Arranged on the inner surface of cylindrical casing 55 and supported by it are the fixed contact segments 61, 62, 63, 64, 65, 66 of current-carrying change-over switch 6 (see FIG. 4), the fixed contacts 111, 112, 113 and 121,

122, 123 of disconnect switches 11 and 12 (see FIGS. 5 and 6) and the fixed contacts 31, 32 of control switch 30 (see FIG. 8). As mentioned above, the electrical function of fulcrums 13, 14, 15 of FIG. 1 may be performed by equivalent fixed slip rings on annular contacts. In FIGS. 2 and 3 reference numerals 13, 14, 15 have been applied to indicate such equivalent slip rings or annular contacts supported on the inner surface of insulating casing 54. The contacts 61 to 66 of FIG. 1 are shown in FIGS. 2 and 4 as consisting of ring segments supported by casing 54. The contacts 111 to 113 of switch 11 of FIG. 1 are also formed by ring segments supported on the inner surface of casing 54 as shown in FIG. 2 and FIG. 5. Similarly the contacts 121 to 126 of switch 12 of FIG. 1 are shown in FIGS. 2 and 6 to consist of contact segments arranged to engage the inner surface of casing 54 and held in position by fasteners projecting transversely through casing 54. In FIG. '2 the radially extending contact arms 67 to 69; 114 to 116 and 124 to 126 of FIG. 1 have been shown to support on the radially outer ends thereof contact bridges extending parallel to the longitudinal axis of casing 54 to which the same reference numerals have been applied as to their equivalent counterparts of FIG. 1. The aforementioned contact bridges 67 to 69; 114 to 116 and 124 to 126 are preferably formed by rollers which are biased radially outwardly by helical springs 58 and supported by pivotable bridge-contactsupporting levers or arms 59 and 60, 60. Arms or levers 59, 60, 60 are provided adjacent the radially outer ends thereof with radially extending recesses for receiving contact-bridge-biasing helical springs 58 biasing contact bridges 67 to 69; 114 to 116 and 124 to 126 radially outwardly into firm engagement with the cooperating fixed contacts thereof and with fixed slip rings or annular contacts 13, 14, 15. FIG. 4 shows clearly roller contact bridges 67 to 69 and their cooperating fixed contacts 61 to 66, and FIG. 5 shows clearly the pins of roller contact bridges 114116 and their cooperating fixed contacts 111- 113. Slip ring or annular contact 13 has only been shown in FIGS. 2 and 3, respectively. The bridge'contact-supporting arms 59 of load-current-carrying change-over switch 6 are of metal, and the bridge contact supporting arms 60 of disconnect switches 11 and 12 are of an insulating material. The bridge contact supporting arms 59, 60, 60 are secured to, and jointly pivotable with, central contact-bridge-operating shaft 57, supported by its upper extension 56 of insulating material. Roller bridge contacts 67 to 69, 114 to 116 and 124 to 126 are adapted to conductively connect one of contact rings or fixed slip rings 13, 14, 15 and one of the aforementioned fixed contacts of switches 6, 11 and 12. In FIG. 4 fixed slip ring or annular contact arranged below contact segments 61 to 66 has not been shown.

Control switch is arranged above switches 6, 11, 12 (FIG. 2). Its fixed contacts 31 and 32 arranged in alternating relation, as shown in FIGS. 1 and 8. An annular contact segment 310 is arranged at a lower level than contacts 31, 32 as clearly shown in FIG. 2. The U-shaped contact springs 320 shown in FIGS. 2 and 8 are biased radially outwardly and thus tend to engage contacts 31, 32 and contact segment 310. Contact springs 320 are supported on the radially outer end of a pivotable contact supporting arms 33 which is, in turn, supported by and jointly pivotable with, insulating shaft 56.

In FIGS. 2 and 7 reference numeral 80 has been applied to indicate pairs of disconnect contacts for conductively connecting components of the system arranged inside of casing such as, for instance, the thyristors 7, 8 and 9, 10 with the switching devices, or switches, 30, 12, 11 and 6 arranged below at lower levels.

Cylindrical casing 54 is closed at its lower end by a bottom plate 540 supporting a bearing 541 for the metal shaft 57 of switches 6, 11, 12. Frame structure 52 for supporting the switch operating spring motor (not shown) may be jointly lifted together with insulating casing 55 and drive shaft 56, 57 and all movable contacts operated by the latter out of cylindrical insulating housing 54. This greatly facilitates inspection and maintenance of the systern.

In FIG. 3 reference character Y has been applied to indicate three terminal studs projecting transversely through casing 54, securing fixed slip ring or annular contact 13 to casing 54 and conductively connecting the forrner to the neutral point of the system or its outgoing line Y.

In FIG. 4 reference characters U V W U V and W have been applied to indicate screw-threaded terminal studs projecting transversely through casing 54 and affixing the fixed contact segments 61 to 66 of switch 6 to the former. Stud U supporting fixed contact 61 is a terminal intended to be conductively connected to tap 1 of winding U, stud V supporting fixed contact 63 is a terminal intended to be conductively connected to tap 1 of winding V, stud W supporting fixed contact 65 is a terminal intended to be conductively connected to tap 1 of winding W, stud U supporting fixed contact 62 is a terminal intended to be conductively connected to tap 2 of winding U, stud V supporting fixed contact 64 is a terminal intended to be conductively connected to tap 2 of Winding V, and stud W supporting fixed Contact 66 is a terminal intended to be conductively connected to tap 2 of winding W.

FIG. 5 shows three screw-threaded studs U V W projecting transversely through casing 54 and securing the fixed contacts of switch 11 to the former. Stud U supporting fixed contact 111 is a terminal intended to be conductively connected to tap 1 of winding U, stud V supporting fixed contact 112 is a terminal intended to be conductively connected to tap 1 of winding V and stud W supporting fixed contact 113 is a terminal intended to be conductively connected to tap 1 of winding W. In FIG. 5 the fixed slip ring or annular contact 14 situated below contacts 111 to 113 has been deleted.

FIG. 6 shows three screw-threaded studs U V W projecting transversely through casing 54 and securing the fixed contacts of switch 12 to the former. Stud U supporting fixed contact 121 is a terminal intended to be conductively connected to tap 2 of winding U, stud V supporting contact 122 is a terminal intended to be conductively connected to tap 2 of winding V, and stud W supporting contact 123 is a terminal intended to be conductively connected to tap 2 of winding W.

If FIG. 2 were sectionalized by horizontal planes to show slip rings or annular contacts 14, 15 of switches 11,

12 in sections, this would result in pictorial representa- 2 tions identical to FIG. 3. Hence it is not deemed necessary to show sections of FIG. 2 along the aforementioned horizontal planes.

Referring now particularly to FIG. 7 the pairs of cooperating disconnect contacts 80 are arranged radially relative to casings 54 and 55. The radially outer contact of each pair of contacts 80 projects radially across casing 54 and has a contact surface situated in the toroidal gap bounded by casings 54 and 55. The radially inner contact of each cooperating pairs of contacts 80 projects radially across casing 55 and is spring-biased radially outwardly into engagement with the contact surface of its cooperating radially outer contact. The pairs of cooperating disconnect contacts 80 make it possible to lift casing 55 and all the parts integral with it for the purpose of inspection and maintenance out of casing 55.

In FIG. 7 reference numerals 7 and 8 have been applied to indicate the radially inner contact of a pair of contacts 80 intended to be conductively connected to thyristors 7 and 8. In like fashion reference numerals 9 and 10 have been applied to indicate the radially inner of a pair of disconnect contacts 80 intended to be conductively connected to thyristors 9 and 10; The radially outer contact of the pair of contacts 80 to which reference numeral 11 has been applied is intended to be conductively connected to switch 11, and more particularly to the slip ring or annular contact 14 thereof (see also FIG. 2). The radially outer contact of the pair of disconnect contacts 80 to which reference numeral 12 has been applied is intended to be conductively connected to switch 11, and more particularly to the slip ring or annular contact 15 thereof (see also FIG. 2). The other cooperating pairs of disconnect contacts 80 are intended to conductively connect other components of the system housed in casing 55 to components of the system housed outside of casing 55.

In FIG. 8 contact 310 arranged below contacts 31 and 32 is not exposed to view since it is arranged in registry with contacts 31 and 32. Reference character E has been applied to indicate a system of leads for conductively connecting the contacts 31 to one of the input terminals of bistable circuitry 34 (FIG. 1). Reference character E has been applied to indicate a system of leads for conductively connecting contacts 32 to the other of the input terminals of bistable circuitry 34.

Reference may be had for further details having a bearing on this invention to U.S. Pat. 3,437,913 to Manfred Matzl, issued Apr. 8, 1969, for Tapped Regulating Transformer Having Thyristor Transfer Switch Means, and to the copending patent application of Manfred Matzl Ser. No. 628,490, filed Apr. 4, 1967, now U.S. Pat. No. 3,466,530, for Logic-Unit-Controlled Thyristor Tapchanging Transfer Switch Having Trigger Impulse Amplifier. The aforementioned patent discloses more in detail a bistable circuit appropriate for the purpose in hand and trigged pulse generators for triggering thyristors. The above copending patent application discloses inter alia a trigger pulse generator for triggeringback-to-back connected pairs of thyristors and the connections between the former and the latter.

It will be apparent that a first triac might be substituted for the pair of inverse parallel connected thyristors 7, 8 and a second triac might be substituted for the pair of inverse parallel connected thyristors 9, 10 without aff cting the system of FIG. 1 and its mode of operation. The term triac is intended to refer to a gate-controlled semiconductor switch for A-C power control. The term gatecontrolled semi-conductor A-C switching device is intended to cover generically both a pair of inverse parallel connected thyristors and a triac.

We claim as our invention:

1. In a three-phase tap-changing transformer system the combination of (a) three tapped transformer windings (U, V, W)

each including a contiguous pair of taps (1, 2);

(b) means establishing a Y-connecting point (Y) for said windings;

(c) integral switch means including two groups of relatively movable contacts (61, 62, 63, 64, 65, 66, 67, 68, 69) for selectively conductively connecting one of said pair of taps (2) of all of said windings (U, V, W) and the other of said pair of taps (1) of all of said windings to said Y-connecting point and for sequentially disconnecting one of said pair of taps and connecting the other of said pair of taps of each of said windings to said Y-connecting point;

((1) a first gate-controlled semi-conductor A-C switching device (7, 8) having a pair of terminals in addition to the gate terminals thereof and a lead conductively connecting one said said pair of terminals of said first semi-conductor A-C switching device to said Y-connecting point;

(e) first disconnect switch means (11) including two groups of relatively movable contacts (111, 112, 113, 114, 115, 116) for selectively connecting the other of said pair of terminals of said first semiconductor A-C switching device (7, 8) to one of said pair of taps 1) of each of said windings (U, V, W) and for disconnecting said other of said pair of terminals of said first semiconductor A-C switching device from any tap of said windings;

(f) a second gate-controlled semiconductor switching device (9, 10) having a pair of terminals in addition to the gate terminals thereof and a lead conductively connecting one of said pair of terminals of said second semiconductor A-C switching device to said Y-connecting point;

(g) a second disconnect switch means (12) including two groups of relatively movable contacts (121, 122, 123, 124, 125, 126) for selectively connecting the other of said pair of terminals of said second semiconductor A-C switching device (9, 10) to the other of said pair of taps (2) of each of said windings (U, V, W) and for disconnecting the other of said pair of terminals of said second semiconductor A-C switching device from any tap of said windings.

2. A device as specified in claim 1 including (a) a first voltage sensing device (37) shunted across said first gate-controlled semiconductor A-C switching device (7, 8);

(b) a second voltage sensing device (38) shunted across said second gate-controlled semiconductor A-C switching device (9, 10); (c) a first trigger pulse generator (39) for triggering said first gate-controlled semiconductor A-C switching device;

(d) a second trigger pulse generator (40) for triggering said second gate-controlled semiconductor A-C switching device (9,

(e) a pair of digital logic elements (35, 36) each having two inputs and one output, the output of one of said pair of logic elements controlling said first trigger pulse generator and the output of the other of said pair of logic elements (36) controlling said second trigger pulse generator and one input of one of said pair of logic elements (35) being supplied by said second voltage sensing device (38) and one input of the other of said pair of logic elements (36) being supplied by said first voltage sensing device (37);

(f) a bistable circuitry (40) having two outputs (A A each supplying the other input of one of said pair of logic elements (35, 36), said bistable circuitry further having two inputs (E E for alternating the states thereof; and

(g) a control switch (30) for alternately energizing one of said two inputs of said bistable circuitry (40) to sequentially alternate the states thereof.

3. A device as specified in claim 1 wherein (a) said integral switch means (6) include six fixed contact segments (61, 62, 63, 64, 65, 66) of difierent length arranged in a circular pattern and three cooperating angularly displaced contacts (67, 68, 69) pivotable about the center of said circular pattern;

(b) said first disconnect switch (11) and said second disconnect switch (12) each includes three fixed contacts (111, 112, 113; 121, 122, 123) arranged in a circular pattern and three cooperating angularly displaced contacts (113, 114, 115; 124, 125, 126) pivotable about the center of said circular pattern;

(c) said integral switch means (6) and said first disconnect switch (11) and said second disconnect switch (12) are synchronously driven by a common shaft (56, 57); and wherein (d) a control switch (30) is synchronously operated by said common shaft (56, 57), said control switch including a plurality of contacts (31, 32) arranged in a circular pattern comprising even contacts (32) and odd contacts (31), said even contacts being conductively interconnected to form a first group of contacts (32) and said odd contacts being conductively interconnected to form a second group of contacts (31) and said control switch further including a contact arm (33) extending radially outwardly from said shaft (56, 57) and alternately engaging contacts of said first group and of said second group upon pivotal motion of said shaft.

4. A device as specified in claim 3 wherein said fixed contact segments (61, 62, 63, 64, 65, 66) of said integral switch means (6), said three fixed contacts (111, 112, 113) of said first disconnect switch (11), said three fixed contacts (121, 122, 123) of said second disconnect switch (12) and said plurality of contacts (31, 32) of said control switch (30) are superimposed and arranged at points of a cylindrical surface at different levels thereof.

5. A device as specified in claim 4 wherein said common shaft (56, 57) includes a lower section (57) of metal and an upper section (56) of insulating material supporting said lower section, said lower section of metal supporting said three contacts (67, 68, 69) of said integral switch means (6), said pivotable contacts (114, 115, 116) of said first disconnect switch( 11) and said pivotable contacts (124, 125, 126) of said second disconnect switch (12) and said upper section of insulating material supporting said contact arm (33) of said control switch 6. A device as specified in claim 3 including (a) a first casing (54) of insulating material supporting at difierent levels thereof said six fixed contact segments (61, 62, 63, 64, 65, 66), said three fixed contacts (111, 112, 113) of said first disconnect switch (11) and said three fixed contacts (122, 123, 124) of said second disconnect switch (12), said casing further supporting three annular contacts (13, 14, 15) arranged at different levels thereof, a first of said annular contacts (13) being arranged adjacent said six fixed contact segments, a second of said annular contacts (14) being arranged adjacent said three fixed contacts of said first disconnect switch, and a third said annular contacts (15) being arranged adjacent said three fixed contacts of said second disconnect switch;

(b) three pivotable angularly displaced roller contacts (67, 68, 69) arranged to engage under spring bias (58) said six fixed contact segments (61, 62, 63, 64, 65, 66) and said first (13) of said annular contacts;

(c) three additional pivotable angularly displaced roller contacts (114, 115, 116) arranged to engage under spring bias (58) said three fixed contacts (111, 112, 113) of said first disconnect switch (11) and said second (14) of said annular contacts; and

(d) three additional pivotable angularly displaced roller contacts (124, 125, 126) arranged to engage under spring bias (58) said three fixed contacts (121, 122, 123) of said second disconnect switch (12) and said third (15) of said annular contacts.

7. A three-phase tap-changing transformer system including (a) three tapped transformer windings (U, V, W) each including a contiguous pair of taps (1, 2);

(b) a load-current-carrying change-over switch (6) having a group of three spaced contacts (67, 68, 69) jointly movable relative to a group of six cooperating contacts (61, 62, 63, 64, 65, 66), said three spaced contacts being conductively interconnected and said six contacts being electrically insulated from each other and each being conductively connected to one of said pair of taps 1, 2) of each of said windings (U, V, W), said three contacts and said six contacts being adapted to selectively connect each of said pair of taps of said windings to a common point (Y) and to disconnect one of said pair of taps and connect the other of said pair of taps of each of said windings to said common point;

(0) a first tripolar disconnect switch (11) having one group of three spaced contacts (114, 115, 116 jointly movable relative to another group of three spaced contacts (111, 112, 113), the constituent contacts of said one group being adapted to sequentially engage one at a time the constituent contacts of said another group and the constituent contacts of said another group being electrically insulated from each other and each of the constituent contacts of said another group being conductively connected to one tap 1) of each pair of taps (1, 2) of each of said windings (U,

(d) a first gate-controlled semiconductor A-C switching device (7, 8) connecting said common point (Y) to said constituent contacts of said one group of contacts (114, 115, 116) of said first disconnect switch (11);

(e) a second tripolar disconnect switch (12) having one group of three spaced contacts (124, 125, 126) jointly movable relative to another group of three spaced contacts (121, 122, 123), the constituent contacts of said one group being adapted to sequentially engage one at a time the constituent contacts of said another group and each of the constituent contacts of said another group being electrically insulated from each other and each of the constituent contacts of said another group being conductively connected to another tap (2) of each pair of taps (1, 2) of each of said windings (U, V, W); and

(f) a second gate-controlled semiconductor A-C switching device (9, connecting said common point (Y) to said constituent contacts of said one group of contacts (124, 125, 126) of said second disconnect switch (12).

8. A system as specified in claim 7 wherein said first gate-controlled semiconductor A-C switching device (7, 8) is formed by a first pair of inverse parallel connected thyristors and wherein said second gate-controlled semiconductor A-C switching device (9, 10) is formed by a second pair of inverse parallel connected thyristors.

9. A system as specified in claim 7 wherein said first gate controlled semiconductor A-C switching device (7, 8) and said second gate controlled semiconductor A-C switching device (9, 10) are each formed by a triac.

10. A system as specified in claim 7 including (a) a first cylindrical casing (54) of insulating material supporting on the inner surface thereof in superimposed layers said group of six spaced contacts (61, 62, 63, 64, 65, 66) of said change-over switch (6), said one group of contacts (111, 112, 113) of said first tripolar 6 disconnect switch (11) and said one group of contacts (121, 122, 123) of said second tripolar disconnect switch (12), said operating shaft (56, 57) being arranged coextensive with the longi tudinal axis of said first casing; and

(b) a second cylindrical casing (55) of insulating material arranged in coaxial relation to said first casing (54), said second casing housing said first gate-controlled semiconductor A-C switching device (7, 8) and said second gate-controlled semiconductor A-C switching device (9, 10) and said second casing defining passage means for the passage of said operating shaft (56, 57) through said second casing.

11. A system as specified in claim 7 wherein (a) said group of six spaced contacts (61, 62, 63, 64, 65, 66) of said change-over switch (6) is fixed and formed by contact segments of difierent length arranged in a circular pattern around a center, and said three spaced contacts (67, 68, 69) of said changeover switch (6) are mounted on and pivoted by an operating shaft (56, 57);

(b) one group of contacts (111, 112, 113) of said first tripolar disconnect switch (11) is fixed and formed by contact segments of dilferent length arranged in a circular pattern around a center and said another group of contacts (114, 115, 116) of said first tripolar disconnect switch (11) is mounted on and pivoted by said operating shaft (56, 57); and

(c) one group of contacts (121, 122, 123) of said second tripolar disconnect switch (12) is fixed and formed by contact segments of different length arranged in a circular pattern around a center and said another group of contacts (124, 125, 126) of said second tripolar disconnect switch (12) is mounted on and pivoted by said operating shaft (56, 57).

12. A system as specified in claim 7 including (a) a first voltage sensing device (37) shunted across said first gate-controlled semiconductor A-C switch ing (7, 8) and including rectifier means (372) for converting A-C inputs into D-C outputs;

(b) a second voltage sensing device (38) shunted across said second gate-controlled semiconductor A-C switching device (9, 10) and including rectifier means (382 for converting A-C inputs into D-C outputs;

(c) a first trigger pulse generator (39) for triggering said first gate-controlled semiconductor A-C switching device (7, 8);

(d) a second trigger pulse generator (40) for triggering said second gate-controlled semiconductor A-C switching device (9, 10);

(e) a pair of AND-gates (35, 36) one controlling said first trigger pulse generator and the other controlling said second triger pulse generator (40), one input of said one (35 of said pair of AND-gates being supplied by said second voltage sensing device (38) and one input of the other (36) of said pair of AND-gates being supplied by said first voltage sensing device (37);

(f) a bistable circuitry (40) having two outputs (A A each supplying the other input of one of said pair of AND-gates (35, 36), said bistable circuitry further having two inputs (E E for alternately changing the state thereof;

(g) a control switch (30) for alternately energizing one of said two inputs (E E of said bistable circuitry; and

(h) common drive means (56, 57) for said load-current-carrying change-over switch (6), said first tripolar disconnect switch (11), said second tripolar disconnect switch (12) and said control switch (30) to synchronously operate said load-current-carrying change-over switch, said first tripolar disconnect switch, said second tripolar disconnect switch and said control switch.

References Cited UNITED STATES PATENTS J D MILLER, Primary Examiner G. GOLDBERG, Assistant Examiner 

